Cabinet for phonographs



July 1, 1941. A. D. BURT CABINET FOR PHONOGRAPHS Filed June 29, 1940(air-r T 63 T I Zinnentor r5510 ttorneg Patented July 2, 1941 J UNITEDSTATES PATENT ,OFFICE CABINET-FOR. PHONOGRAPHS Alexander D. Burt, HaddonHeights, N. J assignor to Radio Corporation of America, a corporation ofDelaware Application June 29, 1940, Serial No. 343,10!v

11 Claims.

This invention relates to cabinets for housing sound-reproducingapparatus, and more particularly to an acoustic filter therein forattenuating sounds of certain frequencies reproduced by phonographshoused therein.

The term phonograph" is usually applied to a system in which a needlefollows the undulations fin the groove of a record and transforms theundulations into corresponding acoustical or electrical variations.Where, for example, an

electrical pickup device is employed in conjunc-- tion with the record,the mechanical variations therein due to the motion of the needle aretransferred to the mechano-electrical transducer and are transformedinto the corresponding electrical variations. The vibration of thevarious elemerits of the pickup and the vibration of the recrd itselfdue 'to the interaction between the Y needle and the record results inthe production of very high intensity sounds by direct transformationfrom. mechanical variations into acoustical variations of the airimmediately surrounding the pickup. Because of the relatively smallsizes of the vibrating elements, most of this energy is confined to thehigh frequency region,.

and the conditions under which this sound is generated generally leadsto considerable distortion-in the sound emanating directly from thepickup and normally reaching'the ear of the listener during operationthereof.

Another object of my present invention is to provide an improved'cabinetas aforesaid which is simple in construction, inexpensive tomanufeature, and highly eflicient in use.

In accordance with my-invention, 1* provide either in the upper ends ofthe walls constituting the body of the cabinet and'against which thecover is adapted to close, or in that portion of the cover itself whichoverlies; the aforementioned wall ends, one or more grooves or slotsrunning lengthwise of the wall edges or running parallel to theperiphery of the cover. Preferably, these groovesshould extendcontinuously all around the cabinet, the grooves cbnstituting acousticcapacitances which are in shunt relation to the acoustic inertanceprovided by the. slight space between the walls of the cabinetandthecover when the cover is closed. If desired, the

space between the cabinet body and the cover may be filled with amaterial providing an acouspickup and the record. Another objectionablefeature found in conventional phonographs of the type underconsideration is that the sound of high frequencies due to themechanical vibration is not in phase with the sound emanating from theloudspeaker connected to the pickup through a suitable amplifier becauseof the short tic resistance, such asfelt. In any case, the resultingarrangement provides alow pass acoustic filter which is very effectiveto attenuate the higher frequencies.

. The novel features that I consider character-- istic of my inventionare set forth with particularity in the appended claims.- The inventionitself, however, both as to its organization and method of operation, aswell as additional objects wave-lengths of the higher frequency sounds.

Also, sounds emitted directly into the-atmosphere as a result of themechanical vibration ofthe pickup device and/or record are notnecessarily harmonically related to the sound produced by theloudspeaker, nor can their volume be cone Thus, when the volume of soundemitted by the loudspeaker is low, that emittedibythe pickup and recordbecome even more noticeable and objectionable. For theforegoing reasons,it

I is desirable to suppress the sound which issues directly from thepickup and record system, and the primary object of my present inventionis to provide an improved phonograph cabinet which will accomplishthispurpose.

More particularly, it is an object of my present invention to provide,in a cabinet for housing ""solmd-reproducing apparatus such as aphonograph, an acoustic filter which will attenuate sounds emanatingdirectly from the record and and advantages thereof, will bestbeunderstood from the following description of several embodimentsthereof, when read in connection with the accompanying drawing, in whichFigure 1 is asectional view of a cabinet according to-one form of myinvention;

Figure 2 is a top elevation of the body portion thereof with the coverremoved, j

form of my invention,

Figure 4 is a fragmentary section of still an other form of myinvention,

Figure 3 is a fragmentary section of another I and a cover B hinged'toone of the walls, such as the wall I, and adapted to overlie the upperends of the walls when the cover B is in closed relation to the body A.The body A is of hollow construction and is provided with a partition ormotor board I upon which is mounted a suitable phonograph which includesa sound-reproducing instrumentality, such as an electrical pickup deviceI I.

Due to manufacturing inaccuracies, warpage in the wood oi which thecabinet is made, and other similar causes, there is a small space Itbetween the cover and the bodyin practically all cabinets. This spacehas been somewhat exaggerated in the drawing by having the cover B reston the hinge II and on a pair of rubber or felt bumpers II.

It is through thisspace that sounds emanatin directly from the pickupdevice II and a record it due to the mechanical vibration thereof passout to the exterior of the cabinet and cause considerabie annoyance,especially at the higher frequencies. a

In order to overcome this diiilculty, I provide one or more grooves orvslots II in the upper ends of each of the walls of the body A inaccordance with the form of my invention shown in Figs. 1 and 2. Theslots 2| runalong the lengths of the upper edges of the walls andcontinue all the way around the cabinet, as clearly shown in Fig. 2. Anysuitable number of slots may be provided and they may be of any desiredwidth and depth.

In any case, the 'slotsll are in shunt relation to the small spaces 23constituting acoustic inertances for the passage of sound waves fromwithductances m1, m, m: and mi correspond to the acoustic inertances ofthe small spaces 23 Just referred to, and 01, ca, correspond to theacoustic capacitances provided by the cavities or grooves II, then theelectrical analogue will be as shown in Fig. 5 wherein it will be notedthat the capacitances c1, c2, 0: are in shunt'relation to the inertancesor inductances mi, 1m, ma, m4, etc. Thus. the acoustic system of Figs. 1and 2 constitutes a low pass filter which will pass only the lowerfrequencies but which will attenuate the higher frequencies.

In the form of my invention shown in Fig. 3, I provide the. slots IIinthe marginal portion of the cover 3, that is, in the portion thereofwhich overlaps the body walls. In other respects, the

provided a novel cabinet which will suppress the l. A cabinet forhousing sound-reproducing apparatus comprising a body portion and acover portion movably associated therewith, said parts having portionsthereof in overlapping relation when said cover is closed with respectto said v body, and at least certain of said overlapping portwo cabinetsare alike, and the operation of the acoustic network in this form of myinvention is the same as in that previously described.

If desired, the grooves ll may be formed both in the ends of the cabinetwalls and in the cover .-B, as shown in Fig. 4. In this case, the twosets as the felt II shown in mg. 4. In the latter case,-

there will be includedin each branch a resistance n. n, etc., inseries-with the inertance mama, etc., as shown in Fig. 6. I

From the foregoing description, it will beapparenttothoseskilledintheartthatIhave'lfi tions being provided with atleast one cavity constituting an acoustic capacitance.

2. A cabinet for housing sound-reproducing apparatus comprising a bodyportion and a cover movably associated therewith, said parts havingportions thereof in overlapping and slightly spaced relation when saidcover is closed with respect to said body, the space between said coverand saidbody permitting the passage of sound waves emanating from saidapparatus out to the exterior of the cabinet and constituting anacoustic inertance therefor, and at least certain of said overlappingportions being provided with one or more cavities constituting acousticcapacitances' adapted to cooperate with said acoustic inertance toattenuate at least a portion of said sound waves.

3. The invention set forth in claim 2 characterized in that saidcavities are arranged in shunt relation to saidspace. i

4. The invention set forth in claim 2 characterized in that the endportion of one of said parts is substantially contiguous to the other ofsaid parts and characterized further in that said cavities areconstituted by one or more grooves formed in said end portion andextending longitudinally thereof.

5. A cabinet for housing sound-reproducing apparatus comprising a bodypart constituted by a plurality of interconnected walls and a coverhinged to one of said walls and adapted to overlie the ends of saidwalls when in closed relation to said body, the ends of said wallsadjacent said cover being provided with one or more grooves extendingalong the lengths-thereof.

6. A cabinet for housing sound-reproducing apparatus comprising a bodypart constituted by a plurality of interconnected walls and a coverhinged to one of said walls and adapted to overlie the ends of saidwalls when in closed relation to said body, the portion of said coverwhich overlies said ends being provided with one .or more groovesextending substantially parallel to the periphery of said cover.v

'7. A cabinet for housing sound-reproducing apparatus comprising a bodypart constituted by a plurality of interconnected walls and a coverhinged to one' of said walls and adapted to overlie the ends of saidwalls when in closed relation to said body, the ends of said wallsadjacent said cover being provided with one or moregrooves extendingalong the. lengths thereof, and the portion of said cover which overliessaid ends being also provided with one' or more grooves extending aroundsaid cover in parallel relation to said first-named grooves.

8. Theinvention set forth in claim 7 characterized in that the groovesin saidwall ends and "the grooves in said cover are arranged in alignedrelation.

9. The invention set forth in claim I characterized in that the groovesin said wall ends and the grooves in said cover are arranged insuperposed relation, and characterized further in that the pair ofgrooves of any superposed set of grooves are each of the same width.

10. A cabinet for housing sound-reproducing apparatus comprising a bodypart and a cover part movably associated therewith, said parts havingportions in overlapp n relation when-said cover is closed with respectto said body and be-

